Adding Bluetooth to DAC90A - UK Vintage Radio Repair and Restoration Discussion Forum

Colin Boggis · 15th Dec 2019, 5:18 pm

I recently restored a very tidy DAC90A and added bluetooth. As I didn't want to modify the wavechange switch or drill holes for an extra switch, plus I wanted it to be possible to easily convert it back to original design I hit upon an alternative way to do it. I made up a sub- assembly with a 5V power supply (transformer, rectifier, regulator) and a long lever micro switch. I mounted this on the dial frame using existing bolts, such that the lever could be bent to be activated when the tuning pointer was at the far left hand end. I made another small pcb to accomodate a mini changeover relay and a Bluetooth module. The only other wiring change made was to disconnect the detector to volume control lead and reconnect it to my new pcb. Another lead went from the pcb to the volume control. When the relay was not activated the detector was connected through to the v/c, and when activated the relay changed over to feed the BT module through. To keep the detector loaded I added a 1Meg resistor from pin 6 of V3 to chassis. Circuitry attached if anyone wants to copy this arrangement.

Ed_Dinning · 15th Dec 2019, 8:01 pm

Hi Colin, please check this circuitry carefully as it may be possible for the bluetooth to be connected directly to the mains via the volume circuitry of the DAC if it is not also run from an isolating transformer.
The bluetooth, even if all insulating materials will not be designed for this sort of connection and could be dangerous.

Ed

ms660 · 15th Dec 2019, 8:13 pm

Ref. the schematic, a chassis connection missing?

Lawrence.

julie_m · 15th Dec 2019, 8:54 pm

By the looks of things, the chassis connection has wrongly been made on the primary side of the transformer. It should be from the circuit's common rail.

The transformer, PSU circuit and Bluetooth module will be live, so should be located entirely inside the radio cabinet.

ms660 · 15th Dec 2019, 9:04 pm

Yes, connecting the Neutral/primary to chassis as shown on the schematic would short out the scale lamps and shunt resistor. I assume Live and Neutral shown is from the switched side of the on/off switch.

Lawrence.

Colin Boggis · 16th Dec 2019, 4:03 pm

I forgot to mention that the mains input has been hard wired to ensure netutral goes to chassis and the pilot bulbs with shunt resistor repositioned in live feed. Thus the primary of the transformer does connect between chassis and switched live. And yes (of course) the bluetooth module is inside the cabinet and just as protected from fingers as the rest of the chassis. Obviously if someone rewires the plug incorrectly it could all become live, but to limit that possibility the mains lead has a moulded plug.

Colin Boggis · 16th Dec 2019, 4:05 pm

Yes ms660, I've also missed off the chassis connection to the DC negative. Sorry! I'll correct the diagram.

ms660 · 16th Dec 2019, 4:17 pm

I would make sure there's a warning notice with a schematic of what you have done attached to the receiver, can't quite figure out why you've put the scale lamps in the Live feed.

Lawrence.

Colin Boggis · 16th Dec 2019, 4:24 pm

Yes updated drawings are with the receiver including the rewired pilot lamps. Circuits attached. The bulbs have been moved because when in the neutral, if one blows, the chassis is potentially live if the shunt resistor is o/c. I also cut out the dial metal around the bulbs and remounted them on an insualting fibreglass panel as the holders not ideal when live if inserted in a panel at neutral potential. It's just my preference to put them in the live.

Colin Boggis · 16th Dec 2019, 4:26 pm

Yes updated drawings are with the receiver including the rewired pilot lamps. Circuits attached. The bulbs have been moved because when in the neutral, if one blows, the chassis is potentially live if the shunt resistor is o/c. I also cut out the dial metal around the bulbs and remounted them on an insualting fibreglass panel as the holders not ideal when live if inserted in a panel at neutral potential. It's just my preference to put them in the live.

15th Dec 2019, 5:18 pm	#1
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Adding Bluetooth to DAC90A I recently restored a very tidy DAC90A and added bluetooth. As I didn't want to modify the wavechange switch or drill holes for an extra switch, plus I wanted it to be possible to easily convert it back to original design I hit upon an alternative way to do it. I made up a sub- assembly with a 5V power supply (transformer, rectifier, regulator) and a long lever micro switch. I mounted this on the dial frame using existing bolts, such that the lever could be bent to be activated when the tuning pointer was at the far left hand end. I made another small pcb to accomodate a mini changeover relay and a Bluetooth module. The only other wiring change made was to disconnect the detector to volume control lead and reconnect it to my new pcb. Another lead went from the pcb to the volume control. When the relay was not activated the detector was connected through to the v/c, and when activated the relay changed over to feed the BT module through. To keep the detector loaded I added a 1Meg resistor from pin 6 of V3 to chassis. Circuitry attached if anyone wants to copy this arrangement. Attached Thumbnails

15th Dec 2019, 8:01 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Adding Bluetooth to DAC90A Hi Colin, please check this circuitry carefully as it may be possible for the bluetooth to be connected directly to the mains via the volume circuitry of the DAC if it is not also run from an isolating transformer. The bluetooth, even if all insulating materials will not be designed for this sort of connection and could be dangerous. Ed

15th Dec 2019, 8:13 pm	#3
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Adding Bluetooth to DAC90A Ref. the schematic, a chassis connection missing? Lawrence.

15th Dec 2019, 8:54 pm	#4
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Adding Bluetooth to DAC90A By the looks of things, the chassis connection has wrongly been made on the primary side of the transformer. It should be from the circuit's common rail. The transformer, PSU circuit and Bluetooth module will be live, so should be located entirely inside the radio cabinet. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

15th Dec 2019, 9:04 pm	#5
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Adding Bluetooth to DAC90A Yes, connecting the Neutral/primary to chassis as shown on the schematic would short out the scale lamps and shunt resistor. I assume Live and Neutral shown is from the switched side of the on/off switch. Lawrence.

16th Dec 2019, 4:03 pm	#6
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Re: Adding Bluetooth to DAC90A I forgot to mention that the mains input has been hard wired to ensure netutral goes to chassis and the pilot bulbs with shunt resistor repositioned in live feed. Thus the primary of the transformer does connect between chassis and switched live. And yes (of course) the bluetooth module is inside the cabinet and just as protected from fingers as the rest of the chassis. Obviously if someone rewires the plug incorrectly it could all become live, but to limit that possibility the mains lead has a moulded plug.

16th Dec 2019, 4:05 pm	#7
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Re: Adding Bluetooth to DAC90A Yes ms660, I've also missed off the chassis connection to the DC negative. Sorry! I'll correct the diagram.

16th Dec 2019, 4:17 pm	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Adding Bluetooth to DAC90A I would make sure there's a warning notice with a schematic of what you have done attached to the receiver, can't quite figure out why you've put the scale lamps in the Live feed. Lawrence.

16th Dec 2019, 4:24 pm	#9
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Re: Adding Bluetooth to DAC90A Yes updated drawings are with the receiver including the rewired pilot lamps. Circuits attached. The bulbs have been moved because when in the neutral, if one blows, the chassis is potentially live if the shunt resistor is o/c. I also cut out the dial metal around the bulbs and remounted them on an insualting fibreglass panel as the holders not ideal when live if inserted in a panel at neutral potential. It's just my preference to put them in the live.

16th Dec 2019, 4:26 pm	#10
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Re: Adding Bluetooth to DAC90A Yes updated drawings are with the receiver including the rewired pilot lamps. Circuits attached. The bulbs have been moved because when in the neutral, if one blows, the chassis is potentially live if the shunt resistor is o/c. I also cut out the dial metal around the bulbs and remounted them on an insualting fibreglass panel as the holders not ideal when live if inserted in a panel at neutral potential. It's just my preference to put them in the live. Attached Thumbnails